1. Field of the Invention
The present invention relates to a process for producing a 2-fluoroisobutyric acid ester. The 2-fluoroisobutyric acid esters obtained by the present process are useful as intermediates of triazine type herbicides.
2. Description of the Prior Arts
WO 90/09378 discloses triazine type herbicides which are triazine derivatives each having a triazine ring substituted with a phenoxyalkylamine group, such as shown by the following formula. ##STR1## According to the document, these triazine type herbicides have remarkable advantages in that they not only show an excellent herbicidal effect but also give no phytotoxicity to paddy rice.
These phenoxyalkylamine group-substituted triazine type herbicides can be obtained by, for example, reacting a 2-fluoroisobutyric acid ester with 2-phenoxy-1-methyl-ethylbiguanide. As the process for production of a 2-fluoroisobutyric acid ester, used in the above reaction, J. Org. Chem. 33 4279 (1968) discloses a process which comprises subjecting a 2-bromoisobutyric acid ester and AgF to a halogen exchange reaction to obtain a 2-fluoroisobutyric acid ester. The reaction is shown by the following reaction formula. ##STR2##
As other process for producing the 2-fluoroisobutyric acid ester, J. Org. Chem. 55 3423 (1990) discloses a process which comprises reacting methyl isobutyrate with trimethylsilyl chloride in the presence of lithium diisopropylamine (LDA) to obtain 1-methoxyl-1-(trimethylsilyloxy)-2-methylpropene and then reacting it with F.sub.2 in CFCl.sub.3 to obtain a 2-fluoroisobutyric acid ester. The reaction is shown by the following reaction formula. ##STR3##
The above conventional process for producing a 2-fluoroisobutyric acid ester from a 2-bromoisobutyric acid ester, however, has had a drawback in that a methacrylic acid ester is generated as a by-product in the process, making low the yield of desired product, i.e. 2-fluoroisobutyric acid ester. The process further has had a drawback in that the AgF used as a reactant in the halogen exchange reaction is expensive, making high the production cost.
The other conventional process for producing a 2-fluoroisobutyric acid ester from methyl isobutyrate, has had a drawback in that the yield of desired product is low because the reaction is conducted in two steps. The process further has had a drawback in that each of the first and second steps must be conducted at an extremely low temperature (-78.degree. C.), requiring a special facility such as refrigerator and the like.